Previous work has demonstrated that in young infants, unlike adults, variations in stimulus bandwidth and frequency do not have equivalent effects on thresholds for long and short duration stimuli. The major objectives of this proposal are to further describe the conditions under which infant's threshold for brief auditory stimuli are markedly different from those of adults, and to identify the mechanisms underlying these differences. A visually-reinforced operant technique will be employed to obtain behavioral thresholds in 6-7 month-old infants; adults will be tested under similar conditions. The proposed studies will 1) provide threshold-duration functions for low- and high-frequency tones and filtered noise; 2) examine spectral integration for long- and short-duration noise bursts; 3) determine the effect of remote masking noise on thresholds for brief stimuli; and 4) investigate the "overshoot" effect associated with the onset of a broadband masker. An additional experiment will examine thresholds for broadband clicks and noise bursts in several age groups to determine when sensitivity to transients approaches maturity. Results of these studies should further our understanding of normal auditory system development and may also contribute to our knowledge of the organization of auditory function in adults. An understanding of the mechanisms involved in sensitivity to transients may be of particular relevance in clinical applications, since procedures most widely used in hearing tests of young infants (e.g. Auditory Brainstem Response) require the use of very brief auditory stimuli.